There have been extensive studies to develop environmentally friend disposable food and beverage containers for fast food based on biodegradable natural polymers and starch. For example, Japanese Laid-open Patent Publication No. Hei 8-311243 discloses a biodegradable foamable composition by compounding a starch polymer, vegetable fibers, metal ions, a blowing agent and an aliphatic polyester.
To impart controlled water-resistivity to such biodegradable polymer compositions, Japanese Laid-open Publication No. Hei 7-97545 discloses a coating agent produced by dissolving a biodegradable aliphatic polyester e.g., polylactic acid, in a halogenated hydrocarbon, e.g., CFC 123 having excellent water resistance and processability. The coating can be applied to a container made of a starch-based material having poor water resistance.
U.S. Pat. No. 6,361,827 provides a method of imparting water resistance to a molded polysaccharide having poor water resistance by bonding to the surface thereof a prolamin such as zein.
Such biodegradable compositions are suitable for a disposable container or package for wrapping fast food having a low moisture content, e.g. hamburger, or dehydrated food. However, the compositions do not provide sufficient resistances to fungi, bacteria and water for a long distribution-storage period, and, in particular, they cannot be used as containers for liquid phase instant food or dehydrated instant food to be cooked with hot water, e.g., cup noodles.